RESUMO
The electron hole spectral width Gamma(h) of Ti 3d states in layered TiTe2 and the inverse lifetime V(i) of the photoelectron final states are determined from experiment within the one-step theory of photoemission. The condition for the possibility of separating the effects of Gamma(h) and V(i) is a strongly non-free-electron character of the final states. The resulting drastic changes of the line shape with photon energy are experimentally observed and explained by an ab initio theory. A nonmonotonic dependence of V(i) on the final-state energy is observed; it is shown to reveal the real space structure of the complex electron self-energy.
RESUMO
The role of the evanescent part of the unoccupied complex band structure in photoemission from surface states is revealed. The frequency dependence of the emission intensity from two surface states on the (100) and (111) surfaces of Al in the photon energy range from 40 to 110 eV is explained within an ab initio one-step theory of photoemission. A novel embedding method to determine surface states is presented. A high sensitivity of surface states spectra to details of the surface potential barrier is predicted, which offers a way to efficiently monitor surface properties.
RESUMO
Mass transport processes on metal surfaces play a key role in epitaxial growth and coarsening processes. They are usually described in terms of independent, statistical diffusion and attachment/detachment of individual metal adatoms or vacancies. Here we present high-speed scanning tunnelling microscopy (video-STM) observations of the dynamic behaviour of five-atom-wide, hexagonally ordered strings of Au atoms embedded in the square lattice of the Au(100)-(1x1) surface that reveal quasi-collective lateral motion of these strings perpendicular to as well as along the string direction. The perpendicular motion can be ascribed to small atomic displacements in the strings induced by propagating kinks, which also provides a mechanism for the exchange of Au atoms between the two string ends, required for motion in string direction. In addition, quasi-one-dimensional transport of Au adatoms along the string boundaries may contribute to the latter phenomenon according to density functional calculations.
Assuntos
Cristalização/métodos , Cristalografia/métodos , Ouro/química , Microscopia de Tunelamento/métodos , Modelos Moleculares , Movimento (Física) , Nanotecnologia/métodos , Simulação por Computador , Difusão , Substâncias Macromoleculares , Metais/química , Microscopia de Vídeo/métodos , Conformação Molecular , Propriedades de SuperfícieRESUMO
The dimensionality of electronic states determines a number of physical phenomena such as phase transitions, transport, or superconductivity. Employing scanning tunneling microscopy combined with angle-resolved photoemission spectroscopy we demonstrate how the dimensionality of electronic states can be continuously tuned from three to two dimensions. This is achieved by adsorption of nanowires on surfaces of layered crystals without changing the chemical composition of the material. Exemplary results for Rb nanowires on TiTe2 are discussed with the help of electronic structure calculations.